It is known in the construction of multi-cylinder in-line internal combustion engines to provide a cylinder head having various components attached thereto, such as manifolds for intake and exhaust gases, secondary combustion air and the like. Separate machined surfaces are often provided for mounting the various components in addition to a mounting face which is secured to the cylinder block and a machined surface provided for the usual rocker or valve cover. In addition, provision may be made for supplying recirculated exhaust gases to one or more of the intake passages. Interconnection of the exhaust and intake manifolds to provide mixture heat may utilize additional machined surfaces. In such engines, design of the manifold passages to obtain substantially equal distribution of the air-fuel mixture to, and volume charging of, the various cylinders is of considerable importance.